THERE’S a theory that if you want a bestseller, you just need to write a book about The Beatles. There’s certainly a huge appetite for books about the Fab Four, and this month International Beatle Week is hosting its first ever Mathew Street Literary Festival. It features talks with authors who have written about all aspects of The Beatles.“We always have a lot of authors who come to the Beatles convention,” says the festival’s musical director Jon Keats.“There have been so many books written about The Beatles, and there was always an element of The Beatles Convention which looked at showcasing the best Beatles authors.